1. Field of the Invention
The present invention relates to oil-from water separators and, more particularly, to systems for preventing oil droplet size reduction when introducing an oil/water stream into an oil-from-water separator.
2. Setting of the Invention
In the production of hydrocarbons from subterranean formations, often times large volumes of water are obtained with the produced oil and gas. Initial processing removes most of the oil and gas from the water; however, significant quantities of oil will still be present in the water. Due to stringent environmental requirements, the oil remaining within the water needs to be separated and removed so that a maximum concentration of oil will be about 48 mg/liter. To meet these stringent environmental requirements, improved hydrocyclone separators and other oil-from-water separation devices are being developed.
Usually, the produced oil/water stream passes into a primary water knockout wherein gas is removed and a major portion of the oil is removed. Thereafter, the oily water passes through a metering or dump valve which limits the quantity of the oil/water stream that is passed to an oil-from-water separation unit. The separation unit usually includes a plurality of hydrocyclone separators, centrifuges, settling tanks or combinations of these.
It has been found that the oil removal efficiency of these separation units is dependent upon the size of oil droplets entering the separation unit. The larger the oil droplet size, the greater the ease of the removal of the oil from the water; conversely, the smaller the oil droplet size, the greater the difficulty in removing the oil from the water. Further, it has been found that the oil droplets are sheared and thus reduced in size when passing through the typical metering valve or dump valve. This phenomenon is described in SPE Paper 18204, "Droplet Size Analysis: A New Tool for Improving Oil Field Separations," by Flanigan et al. published October 1988.
In order to improve the separation efficiency of oil-from-water separation units, there is a need for a system for preventing oil droplet size reduction when introducing an oil/water stream into an oil-from-water separation unit.